Method for flattening and rolling metal powders



E. PODSZUS 3,

METHOD FOR FLATTENING AND ROLLING METAL POWDERS Oct. 3, 1961 Filed March 3, 1953 Fig.3

3,002,254 METHOD FOR FLATTENING AND ROLLING METAL POWDERS Emil Podszus, Lenbachstr. 7, Numberg, Germany Filed Mar. 3, H53, Ser. No. 340,037 15 Claims. (Cl. 29-18) This invention relates to device for flattening and rolling metal powders, and more particularly to produce highly lustrous, extremely thin metal lamellae or flakes, especially suitable for the manufacture of bronze or other metal paints, pigments and the like.

The flattening of granular metal powders to flakes of a thickness which is only a small fraction of the thickness of metal particles obtained by the stamping process, is. made possible by the use of special ball mills provided with baflles and a large number of steel or'like balls. Such ball mills usually contain an extremely large number of steel or like balls, such as, for instance, 80,000 steel balls for each kg. of metal powder. When working, for instance, aluminum powder in such mills the dreaded dust explosions are suppressed by operating in an inert gas atmosphere. This has the further advantage that higher brilliancy and, thus, greater stability are imparted to such powders of fine particle size.

Heretofore, it was not possible to produce powder lame'llae of the brilliancy of highly polished foils. The reason for this is that the metal powder is flattened by the balls in limited portions of the surface which are, strictly speaking point contacts only. Depresssions are continuously formed in the lamellae, so that formation of a truly smooth or plane surface of the powder flakes is not obtained. While a certain smoothing effect is achieved by said depressions gliding and sliding over each other, it is insufficient, particuluarly because breaking and tearing of the flakes at their edges, and consequently undesired pulverisation, cannot be prevented. Similar drawbacks were also encountered when operating according to the stamping process. Unsuccessful attempts were made to use rollers but they did not accomplish the desired. result and the cost of such operation was high.

It is one object of the present invention to eliminate the drawbacks limiting the use of flattening mills and, at the same time, to achieve the advantageous eflects which are accomplished by and connected with such devices in the production of powder in the form of thin lamellae or flakes.

Another object of this invention is to provide flattening bodies in such mills, the shape, dimensions and total surface being such that they do not contact the metal flakes at one point only and that they produce a smoothing and polishing effect.

Other objects of this invention will become apparent from the specification and the detailed description of the invention given therein.

In principle, the device for flattening and rolling metal powder to extremely thin lamellae of high brilliancy according to this invention comprises a closed drum or mill in which a very large number of movable flattening bodies which are polished 'to high brilliancy, are caused to fall and/ or roll freely and, thereby, to flatten the metal powder. The shape, total surface and dimensions of said flattening bodies must be such that the metal powder to be flattened is contacted therewith with sulflcient force and often enough to produce the required very large number of lamellae. Thus, in the case of aluminum, for instance, about flakes per kg. may be produced. The flattening bodies according to this invention, however, do not merely achieve a flattening and pounding effect by point contact as is the case with balls, but they produce a smoothing and polishing effect.

This favorable result is achieved according to the present invention by using flattening bodies of special shape and form, and in a very large number. The central part of said bodies which is responsible for such combined flattening, rolling and polishing effect, is provided with a developable, for instance, a cylindrical surface While the ends of said bodies are of curved, well rounded, preferably of hemispherical shape. The flattening bodies are provided with an extremely fine and brilliant polish and their surfaces must be so smooth that any unevenness between adjacent points on their surface amounts to less than 0.001 mm. Their cross-section need not be of perfectly circular shape. A certain deviation from such shape even increases the gliding and, consequently, the flattening effect. The developable part of said flattening bodies should be made as short as possible so that a very large number of flattening or rolling areas is available, thereby insuring sufficiently thin rolling out or flattening of all metal particles. The surface area of said developable part is preferably half the total surface area of the flattening bodies.

A further feature of this invention consists in using a sufliciently large number of flattening bodies having in toto a correspondingly large surface. The number of flattening bodies and their surface depend upon and are adjusted according to the fineness of the powder to be produced; i.e. the production of finer powders requires a much greater number of flattening bodies and, thus, a much greater total surface than the production of coarser powders. A very large number of flattening bodies is used in the flattening, rolling and polishing procedure. Many thousands of flattening bodies are employed for each kg. of powder to be flattened. The number of flattening bodies does not increase in proportion to the number of powder flakes to be produced nor to their fineness. In the case of aluminum powder, as an average, 10 to 10 flattening bodies are required per kg. of said powder while in the case of heavier powders, a smaller amount is needed, said amount being proportionate to the specific gravity of said heavier powder.

Selection of a proper radius of the curved part of said flattening bodies is also of great importance. Said curvature must be the greater, the finer and thinner the leaflets that are to be produced. Thus, the curvature increases somewhat less than the fineness of the powder increases and the diameter of the bodies decreases. The ratio between surface of the powder to be produced and that of the flattening bodies may serve as an approximate standard of measurement. The total surface area of all the flattening bodies may amount up to only the hundredth part of the surface of the powder to be produced. Thus, said ratio of powder to bodies may be of a magnitude of about :1.

Another important feature of this invention is the propontioning of the length of the developable parts of the flattening bodies with regard to their thickness. The developable parts should be so long and the thickness of the bodies so small that the bodies, on freely falling and/or rolling, will arrange themselves in substantially parallel position to each other. Thereby, a good rolling effect is achieved. Parallel falling is insured when using rather long bodies; the number of eflective points of contact, however, decreases With increased length since each pair of flattening bodies, strictly speaking, possesses only two eifective points of contact. The effectiveness of relatively long bodies is improved by making them very thin and flexible. it is, however, better to provide more rigid bodies with small holes extending therethrough in a longitudinal direction, and to mount several of such substantially uniform flattening bodies loosely in a readily movable manner on long, sufliciently thin and flexible rods or wires.

A very simple and effective shape of the flattening bodies consists in constructing the developable cylindrical part in such a manner that its length is just long enough to cause the bodies to roll predominantly parallel to each other. For this purpose it is sufficient to make the cylindrical part about twice as long as the body is thick. The ends of such bodies are preferably hemispherical since, in general, all angular shapes and structures must be avoided.

The depth to which the flattening drum or mill is filled with the powder is also of importance in order to insure the desired parallel rolling. The most suitable volume to be occupied by the flattening bodies in the mill amounts to about V to about A; of the volume of the mill. The number and size of the bafiles or blades arranged in sm'd mill must also be taken into consideration. They are dependent upon the number and size of the flattening bodies and must be such that not only free fall but also a sliding action of the flattening bodies over each other takes place. The speed of rotation of the flattening mill should not be too high and is preferably adjusted in such a manner that the flattening bodies cooperate with roll parallel to each other without being disturbed by turbulences caused by too high a speed.

The process according to this invention has great advantage and, therefore, is of special importance in the art of producing metal powders because the blackening effect on the powder which is usually encountered in the prior ait stamping process or in the known flattening process by means of balls, is almost completely suppressed. According to the process of this invention the powder particles, when the flattening effect is obtained, becomes polished, but they are not pulverized. The process is of special advantage in the final stages of the flattening operation, for instance, if such flattening is carried out in several steps. The early stages whereby a coarser material is initially flattened may be carried out by milling with balls alone or by hammering or pounding, while in the final stages a fine powder of high brilliancy is produced by means of a device and of flattening bodies according to this invention.

Sometimes it is advisable to add balls to the flattening bodies. Likewise heavy rollers may be added, especially in order to increase the hammering or pounding effect. This is necessary, for instance, when flattening harder materials. The amounts of said larger and/or heavier rollers and/or balls to be added to increase the effectiveness of the flattening device depend, of course, upon the material to be flattened, the size of the flattening device and other factors. In most cases the addition of only a few of such larger and heavier rollers and/or balls is sufficient so that their number and weight are only a fraction of the total number and weight of flattening bodies and preferably do not exceed about of the number and weight of the smaller flattening bodies according to this invention.

The attached drawings serve to illustrate in connection with a rotary mill the invention without, however, limiting the same thereto.

In these drawings:

FIG. 1 is a fragmentary perspective view of one end of a flattening mill wherein the cover is partly broken away to show the interior of said mill;

FIG. 2 is a transverse cross-sectional view through such a flattening mill;

FIGS. 3, 4 and 5 illustrate various shapes of flattening bodies according to this invention;

FIG. 6 illustrates part of a flexible rod having loosely mounted thereon several flattening bodies, and

FIG. 7 is a transverse cross-sectional view taken along line A-A of FIG. 6.

In FIGS. 1 and 2 a flattening mill is illustrated wherein wall 1 of the flattening mill is provided at its end with a flange 2. having holes 3 to receive bolts. Cover 4 of said mill is fastened thereto by bolts 5 passing through corresponding holes in said cover and secured at the reverse side of flange 2 by nuts. Gas inlet 6 is provided in said cover 4 to allow milling in an inert gas, such as nitrogen. At the opposite side of the mill, not shown in the drawing, there are also provided a cover with flange and a gas outlet. Inlets and outlets (not shown) for the material to be flattened and for the flattening bodies are also provided. Since such mills and their operation are well known in the art, it is not necessary to show the means by which they are rotated about their axes. The filling 8 consists of. metal powder and flattening bodies according to this invention which are illustrated more in detail in FIGS. 3 to 7. Usually, such mills are placed on power driven rollers and are rotated thereon. Baflles 7 are radially placed and extend inwardly from the inner surface of wall 1 into the mill.

FIGS. 3, 4, and 5 illustrate flattening bodies of various shape. In FIG. 3 cylindrical part 9 forming the developable surface has a length of about /3 of the overall length of the body while the hemispherical end parts 10 of said body have a radius each of about of said overall length. The diameter of said flattening body is about /s of its overall length. In FIG. 4 the cylindrical part 9 has a length of about ,6 of the overall length, the hemispherical end parts 10 have a length of about of the overall length, and the diameter is about /5 of the overall length. FIG. 5 shows a thicker flattening body having a cylindrical part 9 the length of which is of the overall length, the hemispherical end parts 10 have a length each of about of the overall length, and the diameter is about A: of the overall length.

FIGS. 6 and 7 show part of a rod or wire 11 having loosely mounted thereon several flattening bodies, the purpose of said rod or wire being to hold a number of said flattening bodies in alignment and to insure that they fall parallel to the axis of the drum or mill. Rod or wire 11 is a flexible rod or wire passing through holes formed longitudinally in said bodies. The bodies themselves have a cylindrical part 9 with a developable surface and rounded hemispherical ends 10. The ends 12 of the rod or wire 11 are also rounded and preferably of hemispherical shape, and means may be provided for preventing said bodies from slipping off of said wire.

The size of said flattening bodies is usually smaller than illustrated. Thus, for instance, the overall length of a flattening body may be between about 10 mm. and about 25 mm. and its diameter between about 1 mm. and about 12 mm., while the length of the cylindrical part with developable surface may be between about 6 mm. and about 16 mm. The diameter of the bore hole in FIGS. 6 and 7 may be between about 1 mm. and about 2.5 mm. The diameter of rod 11 may vary between about 0.5 mm. and about 2.2 mm. and its length between about 10 mm. and about 200 mm., thus, carrying between about 3 and about 8 individual flattening bodies. Preferably flattening bodies are employed the diameter of which is about 3-6 mm., the overall length about 8 to 18 mm., and the length of its cylindrical part about 6 to 12 mm.

Of course, also smaller or larger flattening bodies than those mentioned above, may be used. For instance, for producing highly lustrous metal powders preferably flattening bodies having a diameter of only 1 mm. are employed. Usually flattening bodies of about 2.5 to 3 mm. diameter give highly satisfactory results, for instance, with finest aluminum powders. 10 to 10 flattening bodies of this size are required for 1 kg. of such fine aluminum powder. When producing, for instance, aluminum particles up to a particle size of 20 to 30s, the number of flattening bodies is about 100,000 to 1,000,000 times smaller than the number of particles produced. These figures apply to flattening bodies of iron. Tungsten steel gives more favorable results because it is harder and heavier but it is quite expensive so that in many cases it will not be employed. When producing aluminum particles of a particle size of the number of flattening bodies may be reduced to about /3 or the diameter of the flattening bodies may be increased. The amount of powder is preferably so high that, the device being at rest, the powder completely covers the flattening bodies.

For instance, a flattening drum of 1.5 m. length and 1.0 m. diameter, provided with 6 bafiies extending about cm. inwardly, are filled with about 700 kg. of flattening bodies of hardened steel according to the present invention, said flattening bodies having a diameter of about 3 to 6 mm. and an overall length of about 8 to 18 mm. The number of the flattening bodies is between about 10 and about 2x10. 50 kg. of an aluminum powder of a particle size between about 20;/. and about 100,11. are filled into the drum which is then allowed to rotate about its axis with a speed of 30 revolutions per hour. After rotating the drum for about 10 hours the aluminum powder is separated from the flattening bodies. It has a particle size between about 2n and about 30p. and consists of highly lustrous leaflets of a thickness between about 0.2 and about 0.6a while the particles before said flattening treatment had a more compact shape.

The flattening bodies may consist of any suitable hard, heavy, and resistant material, such as steel, especially hardened steel, corundum, tungsten steel, hard ceramic material, such as made from zirconium oxide, and others. For flattening aluminum powder, the flattening bodies are preferably made of hardened steel while the mill itself consists of cast iron, steel or the like. Nitrogen is used with advantage as inert gas.

The device according to this invention is useful not only in flattening and polishing metal powders but may be used for flattening and polishing other materials, such as mica, synthetic resins and others. Addition of small amounts of a lubricant, such as stearin and the like, to the metal powder is advisable and often necessary.

A device for flattening, rolling, and polishing metal and the like powders according to the present invention is well adapted to effect continuous feeding and supplying of the powder to be flattened and discharging of the flattened powder by means of the inert gas introduced into the mill.

The amounts of the above mentioned lubricants added to the metal powder vary depending upon the powder to be flattened and the composition of the lubricant. Of stearin, preferably 1.5% to 2.0% are added when flattening aluminum without, however, limiting the amount of lubricant to such value.

I claim:

1. In the process of producing extremely thin, flat metal and the like powder particles of highest brilliance, wherein pre-comminuted metal and the like particles are continuously subjected to a flattening impact of hard, impactresistant small flattening bodies having a precision-polished, arcuate surface, the step which comprises continuously rolling the pre-comminuted powder particles be-- tween very large numbers of such flattening bodies, said bodies being elongate rolling bodies having a linearly developable central portion of arcuate circumference and of suflicient length to press and roll the particles therebetween while in parallel position to each other, the bodies having arcuate end portions merging with the central portion in arcuate relationship.

2. The process of claim 1, wherein the powder particles are continuously rolled between thousandths of said rolling bodies per kilogram of powder Particles.

3. The process of claim 1, wherein the total surface area of all the rolling bodies is of the order of about one hundredth of the surface area of the powder particles.

4. The process of claim 1, wherein the surface area of the central portion is at least about half the surface area of the entire body.

5. The process of claim 1, wherein the central portion of the rolling bodies is a cylinder having a length approximately twice its diameter and the end portions have a substantially hemispherical shape.

6. In the process of producing extremely thin, flat metal and the like powder particles of highest brilliance, wherein pre-comminuted metal and the like particles are continuously subjected to a flattening impact of hard, impact-resistant small flattening bodies having a precision-polished, arcuate surface, which bodies tumble in a rotating drum, the step which comprises continuously rolling and polishing the pre-comminuted powder particles between very large numbers of tumbling flattening bodies, said bodies being elongate rolling bodies having a linearly developable central portion of arcuate circumference and of suflicient length to press and roll the particles therebetween While in parallel position to each other while they tumble in the rotating drum, the bodies having arcuate end portions merging with the central portion in arcuate relationship.

7. The process of claim 6, wherein the powder particles are continuously rolled and polished between thousands of said rolling bodies per kilogram of powder particles, the number of rolling bodies being up to about 100,000 with increasing fineness of the powder particles.

8. The process of claim 6, wherein the total surface area of all the rolling bodies is of the order of about one hundredth of the surface area of the powder particles.

9. The process of claim 6, wherein the surface area of the central portion is at least about half the surface area of the entire body.

10. The process of claim 6, wherein the central portion of the rolling bodies is a cylinder having a length approximately twice its diameter and the end portions have a substantially hemispherical shape.

11. The process of claim 6, wherein said elongate rolling bodies have a precision-polish of less than 0.001 mm. accuracy.

12. The process of claim 6, wherein the central portion is a cylinder having a length of about 6 to about 16 mm. and a diameter of about 1 to about 12 mm., the end portions being of substantially hemispherical shape and the ratio of diameter to overall length of the body being between about 1:2 and about 1:5.

13. The process of claim 12, wherein the ratio of length of the central cylindrical portion to overall length of the body is between about 2:3 and about 5:6.

14. The process of claim 12, wherein a plurality of said elongate rolling bodies are formed into a unitary structure by mounting them on a thin, flexible rod passing through longitudinal bores in said bodies.

15. The process of claim 14, wherein the rods have a. diameter of about 0.5 to about 2.2 mm., the terminal parts of each rod being of substantially hemispherical shape, and the longitudinal bores in the bodies have a. diameter of about 1 to about 2.5 mm.

References Cited in the file of this patent UNITED STATES PATENTS 983,028 Davidsen Jan. 31, 1911 1,016,272 Johnson Feb. 6, 1912 1,309,212 Marcy July 8, 1919 1,431,475 MacDonald Oct. 10, 1922 1,453,120 Beaver Apr. 24, 1923 1,631,971 Linhard June 14, 1927 1,726,917 North Sept. 3, 1929 1,785,283 Podszus Dec. 16, 1930 2,017,850 Boothman Oct. 22, 1935 2,112,497 Kramer Mar. 29, 1938 2,241,848 Eckart May 13, 1941 2,272,629 Arthur Feb. 10, 1942 2,418,859 Ablett Apr. 15, 1947 2,431,870 Huenerfauth Dec. 2, 1947 2,545,291 Lupo Mar. 13, 1951 2,586,338 Hushley et a1. Feb. 19, 1952 

